The instant invention relates to a system and apparatus for the controlled etching of copper with ferric chloride etchants.
The etching of copper work pieces has attained a fairly sophisticated development. Copper work pieces, for use in electronic circuitry, are successfully etched in the existing art; however, the existing techniques are not considered particularly efficient.
Characteristically, the work piece has been introduced into an etching container and a solution of heated ferric chloride is sprayed onto the surfaces to be etched. Although these solutions are quite effective etchants, the etching procedure itself results in a reduction of the ferric (Fe+++) ions to ferrous (Fe++) ions, the latter being totally ineffective as an etchant. As the etching procedures continue, the concentration of the ferrous ions increases, which condition leads to a decrease in the etching effeciency or speed. Thus, the continuous accretion of copper into the etching solution reduces the ability of the etchant to efficiently perform its function. Therefore an efficient etching process must include provision for removal of the copper from the etchant solution.
The prior art includes systems designed to regenerate the solution. By regeneration, it is meant that one component, such as copper, is removed and the fluid is recycled. The solution is treated, such as exposure to chlorine to bring the solution back to its original potency. In U.S. Pat. No. 3,755,202 to Meek, an elaborate recycling system is described, which essentially functions to remove copper and to regenerate the ferric ions by the introduction of chlorine gas into the solution. This approach, along with others in use, calls for the use of auxiliary equipment that provides the controlled etch rate to be sized on the maximum work load in a given unit of time. If the work load tends to be quite variable, these techniques become quite inefficient; they become costly, use excessive amounts of space and are difficult to handle. Maintenance of the equipment of these systems similarly presents a problem.
The instant invention is designed to satisfy the shortcomings of the existing technology. The fluid is rejuvenated by extracting some of the spent etchant and replacing it with fresh etching fluid. In other words, the excess copper is removed along with some solution; fresh etchant is introduced along with an oxidizer, such as chlorine, to reoxidize the ferrous ions to ferric ions.